Local GABA Receptor Blockade Reveals Hindlimb Responses in the SI Forelimb-Stump Representation of Neonatally Amputated Rats

In adult rats that sustained forelimb amputation on the day of birth, there are numerous multi-unit recording sites in the forelimb-stump representation of primary somatosensory cortex (SI) that also respond to cutaneous stimulation of the hindlimb when cortical receptors for GABA are blocked. These normally suppressed hindlimb inputs originate in the SI hindlimb representation and synapse in the dysgranular cortex before exciting SI forelimb-stump neurons. In our previous studies, GABA (A + B) receptor blockade was achieved by topically applying a bicuculline methiodide/saclofen solution (BMI/SAC) to the cortical surface. This treatment blocks receptors throughout SI and does not allow determination of where along the above circuit the GABA-mediated suppression of hindlimb information occurs. In this study, focal injections of BMI/SAC were delivered to three distinct cortical regions that are involved in the hindlimb-to-forelimb-stump pathway. Blocking GABA receptors in the SI hindlimb representation and in the dysgranular cortex was largely ineffective in revealing hindlimb inputs (∼10% of hindlimb inputs were revealed in both cases). In contrast, when the blockade was targeted at forelimb-stump recording sites, >80% of hindlimb inputs were revealed. Thus GABAergic interneurons within the forelimb-stump representation suppress the expression of reorganized hindlimb inputs to the region. A circuit model incorporating these and previous observations is presented and discussed.

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Suppression of Hindlimb Inputs to S-I Forelimb-Stump Representation of Rats With Neonatal Forelimb Removal: GABA Receptor Blockade and Single-Cell Responses

Journal of Neurophysiology ◽

10.1152/jn.2000.83.6.3377 ◽

2000 ◽

Vol 83 (6) ◽

pp. 3377-3387 ◽

Cited By ~ 14

Author(s):

Andrey S. Stojic ◽

Richard D. Lane ◽

Herbert P. Killackey ◽

Robert W. Rhoades

Keyword(s):

Receptive Field ◽

Gaba Receptors ◽

Cortical Neurons ◽

Gaba Receptor ◽

Single Unit ◽

Receptive Fields ◽

Receptor Blockade ◽

Unit Recording ◽

Cell Responses ◽

Single Cell Responses

Neonatal forelimb removal in rats results in the development of inappropriate hindlimb inputs in the forelimb-stump representation of primary somatosensory cortex (S-I) that are revealed when GABAA and GABAB receptor activity are blocked. Experiments carried out to date have not made clear what information is being suppressed at the level of individual neurons. In this study, three potential ways in which GABA-mediated inhibition could suppress hindlimb expression in the S-I stump representation were evaluated: silencing S-I neurons with dual stump and hindlimb receptive fields, silencing neurons with receptive fields restricted to the hindlimb alone, and/or selective silencing of hindlimb inputs to neurons that normally express a stump receptive field only. These possibilities were tested using single-unit recording techniques to evaluate the receptive fields of S-I forelimb-stump neurons before, during, and after blockade of GABA receptors with bicuculline methiodide (for GABAA) and saclofen (for GABAB). Recordings were also made from normal rats for comparison. Of 92 neurons recorded from the S-I stump representation of neonatally amputated rats, only 2.2% had receptive fields that included the hindlimb prior to GABA receptor blockade. During GABA receptor blockade, 54.3% of these cells became responsive to the hindlimb, and in all but two cases, these same neurons also expressed a stump receptive field. Most of these cells (82.0%) expressed only stump receptive fields prior to GABA receptor blockade. In 71 neurons recorded from normal rats, only 5 became responsive to the hindlimb during GABA receptor blockade. GABA receptor blockade of cortical neurons, in both normal and neonatally amputated rats, resulted in significant enlargements of receptive fields as well as the emergence of receptive fields for neurons that were normally unresponsive. GABA receptor blockade also resulted in increases in both the spontaneous activity and response magnitudes of these neurons. These data support the conclusion that GABA mechanisms generally act to specifically suppress hindlimb inputs to S-I forelimb-stump neurons that normally express a receptive field on the forelimb stump only.

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Intracortical Pathway Involving Dysgranular Cortex Conveys Hindlimb Inputs to S-I Forelimb-Stump Representation of Neonatally Amputated Rats

Journal of Neurophysiology ◽

10.1152/jn.2001.85.1.407 ◽

2001 ◽

Vol 85 (1) ◽

pp. 407-413 ◽

Cited By ~ 8

Author(s):

Andrey S. Stojic ◽

Richard D. Lane ◽

Robert W. Rhoades

Keyword(s):

Somatosensory Cortex ◽

Recent Work ◽

Gaba Receptors ◽

Gaba Receptor ◽

Cobalt Chloride ◽

Primary Somatosensory Cortex ◽

Receptor Blockade ◽

Neuronal Circuit ◽

Treatment Results

Reorganization of the primary somatosensory cortex (S-I) forelimb-stump representation of rats that sustained neonatal forelimb removal is characterized by the expression of hindlimb inputs that are revealed when cortical GABA receptors are pharmacologically blocked. Recent work has shown that the majority of these inputs are transmitted from the S-I hindlimb representation to the forelimb-stump field via an, as yet, unidentified pathway between these regions. In this study, we tested the possibility that hindlimb inputs to the S-I forelimb-stump representation of neonatally amputated rats are conveyed through an intracortical pathway between the S-I hindlimb and forelimb-stump representations that involves the intervening dysgranular cortex by transiently inactivating this area and evaluating the effect on hindlimb expression in the S-I forelimb-stump representation during GABA receptor blockade. Of 332 S-I forelimb-stump recording sites from six neonatally amputated rats, 68.3% expressed hindlimb inputs during GABA receptor blockade. Inactivation of dysgranular cortex with cobalt chloride (CoCl2) resulted in a significant decrease in the number of hindlimb responsive sites (9.5%, P < 0.001 vs. cortex during GABA receptor blockade before CoCl2 treatment). Results were also compiled from S-I forelimb recording sites from three normal rats: 14.1% of 136 sites were responsive to the hindlimb during GABA receptor blockade, and all of these responses were abolished during inactivation of dysgranular cortex with CoCl2 ( P < 0.05). These results indicate that the S-I hindlimb representation transmits inputs to the forelimb-stump field of neonatally amputated rats through a polysynaptic intracortical pathway involving dysgranular cortex. Furthermore the findings from normal rats suggest that this pathway might reflect the amplification of a neuronal circuit normally present between the two representations.

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Role of Development in Reorganization of the SI Forelimb-Stump Representation in Fetally, Neonatally, and Adult Amputated Rats

Journal of Neurophysiology ◽

10.1152/jn.00065.2003 ◽

2003 ◽

Vol 90 (3) ◽

pp. 1842-1851 ◽

Cited By ~ 8

Author(s):

Charles P. Pluto ◽

Richard D. Lane ◽

Nicolas L. Chiaia ◽

Andrey S. Stojic ◽

Robert W. Rhoades

Keyword(s):

Receptive Field ◽

Somatosensory Cortex ◽

Gaba Receptors ◽

Cobalt Chloride ◽

Unit Recording ◽

Lower Jaw ◽

Age Dependent ◽

The Face ◽

Stimulation Of

Rats that sustain forelimb removal on postnatal day (P) 0 exhibit numerous multi-unit recording sites in the forelimb-stump representation of primary somatosensory cortex (SI) that also respond to hindlimb stimulation when cortical GABAA+B receptors are blocked. Most of these hindlimb inputs originate in the medial SI hindlimb representation. Although many forelimb-stump sites in these animals respond to hindlimb stimulation, very few respond to stimulation of the face (vibrissae or lower jaw), which is represented in SI just lateral to the forelimb. The lateral to medial development of SI may influence the capacity of hindlimb (but not face) inputs to “invade” the forelimb-stump region in neonatal amputees. The SI forelimb-stump was mapped in adult (>60 days) rats that had sustained amputation on embryonic day (E) 16, on P0, or during adulthood. GABA receptors were blocked and subsequent mapping revealed increases in nonstump inputs in E16 and P0 amputees: fetal amputees exhibited forelimb-stump sites responsive to face (34%), hindlimb (10%), and both (22%); neonatal amputees exhibited 10% face, 39% hindlimb, and 5% both; adult amputees exhibited 10% face, 5% hindlimb, and 0% both, with ∼80% stump-only sites. These results indicate age-dependent differences in receptive-field reorganization of the forelimb-stump representation, which may reflect the spatiotemporal development of SI. Results from cobalt chloride inactivation of the SI vibrissae region and electrolesioning of the dysgranular cortex suggest that normally suppressed vibrissae inputs to the SI forelimb-stump area originate in the SI vibrissae region and synapse in the dysgranular cortex.

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Altered Expression of GABAergic Markers in the Forebrain of Young and Adult Engrailed-2 Knockout Mice

Genes ◽

10.3390/genes11040384 ◽

2020 ◽

Vol 11 (4) ◽

pp. 384

Author(s):

Giovanni Provenzano ◽

Angela Gilardoni ◽

Marika Maggia ◽

Mattia Pernigo ◽

Paola Sgadò ◽

...

Keyword(s):

Gaba Receptors ◽

Gaba Receptor ◽

Brain Regions ◽

Autism Spectrum ◽

Gabaergic Interneuron ◽

Gabaergic Interneurons ◽

Rt Pcr ◽

Altered Expression ◽

Gabaergic Neurotransmission ◽

Adult Mice

Impaired function of GABAergic interneurons, and the subsequent alteration of excitation/inhibition balance, is thought to contribute to autism spectrum disorders (ASD). Altered numbers of GABAergic interneurons and reduced expression of GABA receptors has been detected in the brain of ASD subjects and mouse models of ASD. We previously showed a reduced expression of GABAergic interneuron markers parvalbumin (PV) and somatostatin (SST) in the forebrain of adult mice lacking the Engrailed2 gene (En2-/- mice). Here, we extended this analysis to postnatal day (P) 30 by using in situ hybridization, immunohistochemistry, and quantitative RT-PCR to study the expression of GABAergic interneuron markers in the hippocampus and somatosensory cortex of En2-/- and wild type (WT) mice. In addition, GABA receptor subunit mRNA expression was investigated by quantitative RT-PCR in the same brain regions of P30 and adult En2-/- and WT mice. As observed in adult animals, PV and SST expression was decreased in En2-/- forebrain of P30 mice. The expression of GABA receptor subunits (including the ASD-relevant Gabrb3) was also altered in young and adult En2-/- forebrain. Our results suggest that GABAergic neurotransmission deficits are already evident at P30, confirming that neurodevelopmental defects of GABAergic interneurons occur in the En2 mouse model of ASD.

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Blockade of GABAergic Inhibition Reveals Reordered Cortical Somatotopic Maps in Rats That Sustained Neonatal Forelimb Removal

Journal of Neurophysiology ◽

10.1152/jn.1997.77.5.2723 ◽

1997 ◽

Vol 77 (5) ◽

pp. 2723-2735 ◽

Cited By ~ 22

Author(s):

Richard D. Lane ◽

Herbert P. Killackey ◽

Robert W. Rhoades

Keyword(s):

Gaba Receptor ◽

Receptive Fields ◽

Projection Neurons ◽

Cortical Region ◽

Gabaergic Inhibition ◽

Adult Rats ◽

Inhibitory Mechanisms ◽

Significant Difference ◽

Stimulation Of

Lane, Richard D., Herbert P. Killackey, and Robert W. Rhoades. Blockade of GABAergic inhibition reveals reordered cortical somatotopic maps in rats that sustained neonatal forelimb removal. J. Neurophysiol. 77: 2723–2735, 1997. A previous study from this laboratory demonstrated that forelimb removal at birth results in invasion of the cuneate nucleus (CN) by sciatic nerve axons and the development of CN cells including thalamic projection neurons with receptive fields that include both the forelimb stump and the hindlimb. However, recordings from unit clusters in lamina IV of the primary somatosensory cortex (SI) of these animals revealed the presence of only a very few sites in the forelimb stump representation where responses to hindlimb stimulation could also be recorded. In the present study we tested the possibility that input from the hindlimb was suppressed in lamina IV of the cortical stump representation via GABAergic inhibitory mechanisms by mapping this cortical region, applying the γ-aminobutyric acid-A (GABAA) and GABAB receptor antagonists bicuculline and phaclofen (50 μM each), and then remapping the same sites. In six neonatally manipulated rats, 15 of 242 sites (6.2%) in the stump representation responded to hindlimb stimulation before GABA receptor blockade and 107 (44.2%) of the same sites responded to stimulation of the hindlimb during blockade ( P < 0.05). In six normal adult rats, 7 of 264 sites (2.7%) in the forelimb representation responded to hindlimb stimulation before the application of bicuculline and phaclofen. During GABA receptor blockage, 31 of these sites (11.7%) responded to such stimulation ( P < 0.02 vs. the untreated normal cortex and P < 0.01 vs. the neonatally manipulated rats treated with GABA blockers). To specifically test the role of GABAA versus GABAB receptors in the inhibition of hindlimb input to the SI stump representation in rats that sustained neonatal forelimb removal, either bicuculline or phaclofen alone was applied to SI in nine neonatally manipulated animals. In four rats treated with bicuculline, 12 of 184 sites (6.5%) in the stump representation responded to hindlimb stimulation before treatment and 61 of 184 sites (33.2%) responded to such stimulation during application ( P < 0.01). In animals ( n = 5) treated with phaclofen, 18 of 251 sites (7.2%) responded to hindlimb stimulation before treatment and 64 of these sites (25.5%) responded to such stimulation during application ( P < 0.05). There was no significant difference between the results obtained with bicuculline alone, phaclofen alone, or the two GABA blockers delivered together ( P > 0.05). These results indicate that hindlimb input to the portion of SI representing the forelimb stump is functionally suppressed in rats that have sustained neonatal forelimb removal and that GABAergic inhibition, mediated by both GABAA and GABAB receptors, is involved in this process.

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Spinal cord GABA receptors modulate the exercise pressor reflex in decerebrate rats

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.00140.2013 ◽

2013 ◽

Vol 305 (1) ◽

pp. R42-R49 ◽

Cited By ~ 12

Author(s):

Han-Jun Wang ◽

Wei Wang ◽

Kaushik P. Patel ◽

George J. Rozanski ◽

Irving H. Zucker

Keyword(s):

Spinal Cord ◽

Dorsal Horn ◽

Gaba Receptors ◽

Gaba Receptor ◽

Pressor Response ◽

Central Component ◽

Gaba A ◽

Exercise Pressor Reflex ◽

Dorsal Horns ◽

Pressor Reflex

Neurotransmitters and neuromodulators released by contraction-activated skeletal muscle afferents into the dorsal horn of the spinal cord initiate the central component of the exercise pressor reflex (EPR). Whether γ-aminobutyric acid (GABA), a major inhibitory neurotransmitter within the mammalian central nervous system, is involved in the modulation of the EPR at the level of dorsal horn remains to be determined. We performed local microinjection of either the GABA(A) antagonist bicuculline or the GABA(B) antagonist CGP 52432 into the ipisilateral L4/L5 dorsal horns to investigate the effect of GABA receptor blockade on the pressor response to either static contraction induced by stimulation of the peripheral end of L4/L5 ventral roots, passive stretch, or hindlimb arterial injection of capsaicin (0.1 μg/0.2 ml) in decerebrate rats. Microinjection of either bicuculline (1 mM, 100 nl) or CGP 52432 (10 mM, 100 nl) into the L4/5 dorsal horns significantly increased the pressor and cardioaccelerator responses to all stimuli. Microinjection of either bicuculline or CGP 52432 into the L5 dorsal horn significantly increased the pressor and cardioaccelerator responses to direct microinjection of l-glutatmate (10 mM, 100 nl) into this spinal segment. The disinhibitory effect of both GABA receptor antagonists on the EPR was abolished by microinjection of the broad-spectrum glutamate receptor antagonist kynurenate (10 mM/100 nl). These data suggest that 1) GABA exerts a tonic inhibition of the EPR at the level of dorsal horn; and 2) that an interaction between glutamatergic and GABAergic inputs exist at the level of dorsal horn, contributing to spinal control of the EPR.

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ADENOHYPOPHYSEAL LH CONTENT IN NORMAL, ANDROGEN-STERILIZED AND PROGESTERONE-PRIMED STERILE FEMALE RATS

Acta Endocrinologica ◽

10.1530/acta.0.0390013 ◽

1962 ◽

Vol 39 (1) ◽

pp. 13-21 ◽

Cited By ~ 19

Author(s):

Roger A. Gorski ◽

Charles A. Barraclough

Keyword(s):

Ascorbic Acid ◽

Electrical Stimulation ◽

Quantitative Determination ◽

Median Eminence ◽

Hypothalamic Stimulation ◽

Female Rats ◽

Rat Pituitary ◽

Gland Content ◽

Stimulation Of

ABSTRACT We have previously suggested that the failure of the androgen-sterilized, persistent-oestrous rat to ovulate, following electrical stimulation of the median eminence structures of the hypothalamus, is due to an insufficiency in adenohypophyseal LH concentration. Using the ovarian ascorbic acid technique for quantitative determination of pituitary LH content, the present studies have demonstrated that the sterile rat pituitary gland contains one-third the LH content of the normal prooestrous gland. Furthermore, not only does progesterone priming of this persistent-oestrous rat result in a 75 % increase in LH concentration, but on hypothalamic stimulation sufficient LH is released to induce ovulation. The decrease in LH concentration which accompanies ovulation in the progesterone-primed, sterile rat is approximately 45 % of the total gland content as compared with a 51 % decrease in pituitary content in the normal cyclic rat.

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CATECHOLAMINE ANTAGONISM TO OXYTOCIN-INDUCED MILK-EJECTION

Acta Endocrinologica ◽

10.1530/acta.0.067s005 ◽

1971 ◽

Vol 68 (1_Suppla) ◽

pp. S5-S38 ◽

Cited By ~ 14

Author(s):

Helmuth Vorherr

Keyword(s):

Receptor Blockade ◽

Milk Ejection ◽

Beta Adrenergic ◽

Beta Receptor ◽

Beta Receptors ◽

Alpha Receptors ◽

Adrenergic Blockers ◽

Beta Receptor Blockade ◽

Second Pain ◽

Stimulation Of

ABSTRACT In lactating rats and rabbits the mode of antagonism of sympathomimetics, angiotensin or pain toward oxytocin-induced milk-ejection was investigated. In rats intra-arterial (intrafemoral) doses of 0.01–0.02 μg or intravenous (iv) doses of 0.1–0.5 μg of either epinephrine, isoproterenol, norepinephrine, angiotensin or 10 μg of phenylephrine injected simultaneously with, or 30 seconds before an oxytocin dose (10 μU intrafemoral, 300 μU iv) greatly inhibited or suppressed the oxytocin response. A 15 second pain stimulus caused moderate inhibition. With alpha-receptor blockade pain, epinephrine, isoproterenol, norepinephrine, phenylephrine and angiotensin inhibition were, respectively, 70%, 75%, 100%, 40%, 0% and 100%. Under beta-receptor blockade the corresponding values were 14%, 40%, 0%, 70%, 100% and 100%; with simultaneous intrafemoral injections neither catecholamine was inhibitory toward oxytocin. In corresponding rabbit experiments approximately 10-fold higher iv drug dosages were applied and similar results were observed. In both species, combined alpha and beta-receptor blockade nearly eliminated the antagonistic actions of sympathomimetics toward oxytocin, whereas angiotensin inhibition persisted unchanged. The results indicate: 1) Mammary myoepithelial cells contain beta-adrenergic receptors but no alpha-receptors; 2) Inhibition of oxytocin-induced milk-ejection by isoproterenol and phenylephrine is meditated through stimulation of myoepithelial beta-receptors (myoepithelial relaxation) and vascular alpha-receptors (vasoconstriction), respectively; 3) Epinephrine and norepinephrine inhibition of milk-ejection is due to stimulation of vascular alpha-receptors and myoepithelial beta-receptors; 4) Angiotensin effects are unrelated to adrenergic receptor mechanisms; 5) Administration of both alpha and beta-adrenergic blockers is desirable for stabilizing the sensitivity of the oxytocin milk-ejection assay preparation against interference from endogenous or exogenous catecholamines; 6) Other than using adrenergic blockers, pharmacologic doses of oxytocin can correct nursing difficulties in animals and man with hyperfunction of the adrenal-sympathetic system.

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